package com.fallsvc.re.networkprogramming.socket.Udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    // 参数是服务器要绑定的端⼝
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    // 使⽤这个⽅法启动服务器.
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
// 反复的, ⻓期的执⾏针对客⼾端请求处理的逻辑.
// ⼀个服务器, 运⾏过程中, 要做的事情, 主要是三个核⼼环节.
// 1. 读取请求, 并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
// 这样的转字符串的前提是, 后续客⼾端发的数据就是⼀个⽂本的字符串.
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
// 2. 根据请求, 计算出响应
            String response = process(request);
// 3. 把响应写回给客⼾端
// 此时需要告知⽹卡, 要发的内容是啥, 要发给谁.
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.length(),
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
// 记录⽇志, ⽅便观察程序执⾏效果.
            System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress(), requestPacket.getPort(),
                    request, response);
        }

    }

    // 根据请求计算响应. 由于是回显程序, 响应内容和请求完全⼀样.
    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}